From: Anthony Liguori <anthony@codemonkey.ws>
To: Rusty Russell <rusty@rustcorp.com.au>,
"Michael S. Tsirkin" <mst@redhat.com>,
Thomas Lendacky <tahm@linux.vnet.ibm.com>
Cc: Sasha Levin <levinsasha928@gmail.com>,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, avi@redhat.com,
kvm@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH 0/3] virtio-net: inline header support
Date: Wed, 03 Oct 2012 20:24:47 -0500 [thread overview]
Message-ID: <87mx033u74.fsf@codemonkey.ws> (raw)
In-Reply-To: <87vces2gxq.fsf@rustcorp.com.au>
Rusty Russell <rusty@rustcorp.com.au> writes:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
>
>> Thinking about Sasha's patches, we can reduce ring usage
>> for virtio net small packets dramatically if we put
>> virtio net header inline with the data.
>> This can be done for free in case guest net stack allocated
>> extra head room for the packet, and I don't see
>> why would this have any downsides.
>
> I've been wanting to do this for the longest time... but...
>
>> Even though with my recent patches qemu
>> no longer requires header to be the first s/g element,
>> we need a new feature bit to detect this.
>> A trivial qemu patch will be sent separately.
>
> There's a reason I haven't done this. I really, really dislike "my
> implemention isn't broken" feature bits. We could have an infinite
> number of them, for each bug in each device.
This is a bug in the specification.
The QEMU implementation pre-dates the specification. All of the actual
implementations of virtio relied on the semantics of s/g elements and
still do.
What's in the specification really doesn't matter when it doesn't agree
with all of the existing implementations.
Users use implementations, not specifications. The specification really
ought to be changed here.
Regards,
Anthony Liguori
next prev parent reply other threads:[~2012-10-04 1:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-28 9:26 [PATCH 0/3] virtio-net: inline header support Michael S. Tsirkin
2012-09-28 9:26 ` [PATCH 1/3] virtio: add API to query ring capacity Michael S. Tsirkin
2012-09-28 9:26 ` [PATCH 2/3] virtio-net: correct capacity math on ring full Michael S. Tsirkin
2012-10-04 0:24 ` Rusty Russell
2012-09-28 9:26 ` [PATCH 3/3] virtio-net: put virtio net header inline with data Michael S. Tsirkin
2012-10-03 6:44 ` [PATCH 0/3] virtio-net: inline header support Rusty Russell
2012-10-03 7:10 ` Rusty Russell
2012-10-04 1:24 ` Anthony Liguori [this message]
2012-10-04 3:34 ` Rusty Russell
2012-10-04 4:29 ` Anthony Liguori
2012-10-04 7:44 ` Rusty Russell
2012-10-05 7:47 ` Paolo Bonzini
2012-10-08 21:31 ` Michael S. Tsirkin
2012-10-04 1:35 ` Anthony Liguori
2012-10-04 5:17 ` Rusty Russell
2012-10-08 20:41 ` Michael S. Tsirkin
[not found] ` <87vces2gxq.fsf__45058.6618776017$1349247807$gmane$org@rustcorp.com.au>
2012-10-03 10:53 ` Paolo Bonzini
2012-10-04 0:11 ` Rusty Russell
2012-10-04 7:09 ` Paolo Bonzini
2012-10-04 12:51 ` Rusty Russell
2012-10-04 13:23 ` Paolo Bonzini
2012-10-05 5:43 ` Rusty Russell
[not found] ` <87391t1nkq.fsf__40391.6521034718$1349505001$gmane$org@rustcorp.com.au>
2012-10-06 12:54 ` Paolo Bonzini
2012-10-09 4:59 ` Rusty Russell
2012-10-09 7:27 ` Paolo Bonzini
2012-10-11 0:03 ` Rusty Russell
2012-10-11 11:04 ` Michael S. Tsirkin
2012-10-11 22:37 ` Rusty Russell
2012-10-12 7:38 ` Paolo Bonzini
2012-10-12 11:52 ` Cornelia Huck
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